Underbody liners as a rule are planar structures whose thickness direction has considerably smaller dimensions than the two main extension directions, orthogonal both to the thickness direction and the one another, of the planar underbody liner. The planar configuration furthermore does not preclude the underbody liner as a whole from being of three-dimensional conformation, i.e. from being planar but not necessarily flat.
At least three objectives are pursued with an underbody liner on a vehicle: firstly, the underbody of the vehicle is to be protected from mechanical effects, for example stone impacts and the like. Secondly, the underbody liner often provides acoustic insulation for a vehicle, the underbody liner being intended both to decrease the vehicle's acoustic emissions and to decrease the penetration of noise from outside into the vehicle passenger compartment. Third, the underbody liner is intended to improve the vehicle's aerodynamics by the fact that the underbody liner creates a smoother or less-profiled lower terminating surface of a vehicle than would be the case without mounting of an underbody liner.
In the context of mounting of an underbody liner component that is intended to furnish a maximally smooth, flat lower terminating surface on the vehicle, locally different height differences between the lower outer surface (liner surface) of the underbody liner component and the vehicle underbody often need to be spanned. Boss-like bulges that extend away from what is later the lower outer surface of the underbody liner are often configured for that purpose on the underbody liner component. These boss-like bulges are also referred to in the present Application as “fastening bosses.”
These boss-like bulges, constituting an installation configuration for connecting the underbody liner component to a vehicle underbody, generally taper in a direction away from the lower terminating surface of the underbody liner toward the vehicle underbody. An installation segment that is located in the boss-like bulge farther from what is later the lower terminating surface of the underbody liner, and is generally flat, has as a rule an installation opening, passing completely through it in a thickness direction, which is penetrated by a fastening means when the underbody liner is in the fully installed state. The fastening means generally braces against the installation segment in the vicinity of the installation opening.
In order to increase the tear-out resistance of the installation segment, as a rule a washer is arranged between the installation segment and the fastening means, in order to increase the area over which the fastening means exerts force onto the underbody liner component.
The boss-like bulged-out fastening bosses of the underbody liner component have, in what is later the terminating surface of the underbody liner fully installed on the vehicle, a considerable opening that disrupts the aerodynamic effect of the underbody liner component. Ideally, the lower terminating surface of a motor vehicle is as flat as possible. As a rule, the greater the deviation of the lower terminating surface from the flat state, the greater the deviation of the aerodynamic effect of the underbody liner component from the desired optimal aerodynamic effect.